OpenAPI is a set of standards to help you define and create modern APIs that are machine readable and can be easily consumed. There is a large amount of quality tooling available to you if you choose to create your APIs in such a way. There are also a number of benefits from being able to make machine readable API specifications including:
Knowledge transfer, especially when considering compatibility concerns, is greatly improved by well documented APIs. As such we have found that using machine readable API specifications has greatly improved our productivity when we are making and consuming APIs.